Anti-phospholipid antibodies are a type of autoantibody associated with significant cardiovascular pathology, stroke, and recurrent miscarriages. It is not known how these antibodies arise, or whether T cells are involved in their generation. CD1d-restricted T cells are a novel population of T lymphocytes that recognize lipid and glycolipid antigens, including in some cases phospholipids. CD1d molecules are expressed on antigen presenting cells, including B cells. This proposal investigates the hypothesis that anti-phospholipid antibody production by B cells could be regulated by CD1d-restricted T cells in an antigen specific manner. The analysis focuses on whether the presence of elevated levels of pathogenic anti-phospholipid antibodies correlates with changes in the numbers, activation states, functions, or antigen specificities of CD1d-restricted T cells. This will be assessed in the following specific aims: i) flow cytometric analysis will be performed using lipid antigen loaded CD1d tetramers to detect and analyze the functional properties of CD1d-restricted T cells from peripheral blood of patients with anti-phospholipid antibodies compared to control donors; ii) binding of different phospholipids to CD1d molecules will be analyzed using CD1d-Fc fusion proteins and fluorescent or radiolabeled phospholipids; iii) CD1d-restricted T cell clones will be derived from patients with anti-phospholipid antibodies and control donors, and used to investigate reactivity to individual phospholipids, and to test recognition of anti-phospholipid antibody producing B cells. This investigation will provide new insight into the role of autoreactive T cells in the generation of autoantibodies, and may provide new diagnostic and therapeutic approaches for conditions associated with pathogenic anti-phospholipid antibodies.